Laws and social norms exist to moderate the behavior of individuals so that society as a whole thrives. If we don't suppress harmful behavior then it will destabilize society.
This line that shouldn't be crossed is obvious in things like assault, rape, and other actions that directly disrupt people's autonomy. The line gets blurrier and more difficult to define when actions indirectly disrupt autonomy.
It's also important to note the effect of social media on violent social contagion. I was on 4chan between the years of 2011 and 2013. At the time, they formed a community that supported and glorified violence, school shootings, and eventually Nazis. I'm positive that such contagion contributed significantly to both our school shootings and current political instability.